Trovafloxacin was found to be a typical quinolone producing a biphasic dose response against Escherichia coli, Staphylococcus aureus or Streptococcus pneumoniae. A reduced rate of kill was seen against Enterococcus faecalis, which is also typical of the quinolones. However, the bactericidal activity of trovafloxacin against S. aureus and S. pneumoniae was greater than most other quinolones previously tested. The enhanced bactericidal activity of trovafloxacin against S. aureus may be explained by the possession of a very strong bactericidal mechanism B. Trovafloxacin may prove to be a quinolone of choice against S. aureus infections.